The compounds of claim 2, wherein R2 is a member selected from the class consisting of C1-9 alkyl, C3-6 cycloalkyl, C6-10 aryl, C7-10 aralkyl, C7-10 cycloalkylalkyl and R' is a member selected from the class consisting of 1-naphthyl substituted with a member selected from the class consisting of alkoxy and alkoxycarbonyloxy, respectively containing not more than 5 carbon atoms and 2-naphthyl subst